Figure 4b. Tumor of the retromolar trigone with involvement of the buccal mucosa and buccinator muscle. (a) Axial T1-weighted MR image obtained with a cannula in the mouth shows separation of the buccal mucosal surface involved by a tumor (black arrow) and the gingival mucosal surfaces (white arrow). * = signal void of the cannula. (b) Axial T1-weighted MR image obtained with fat saturation and gadolinium contrast material shows the extent of the tumor and the buccal involvement (arrows). (c) Photograph obtained during direct examination of the oral cavity shows the involvement of the buccal mucosa.